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The female platypus has a pair of ovaries, but only the left one is functional. It lays one to three (usually two) small, leathery eggs (similar to those of reptiles), about 11 mm (0.43 in) in diameter and slightly rounder than bird eggs. The eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). After laying her eggs, the female curls around them. The incubation period is divided into three phases. In the first phase, the embryo has no functional organs and relies on the yolk sac for sustenance. The yolk is absorbed by the developing young. During the second phase, the digits develop and, in the last phase, the egg tooth appears.

The newly hatched young are vulnerable, blind, and hairless, and are fed by the mother's milk. Although possessing m…

* The gestation period of the narwhal is generally between 10-16 months * Baby narwhals are referred to as "calves
* These calves are brown and have no spots, while the adult narwhals are blue-gray with white spots
* Narwhal calves are nursed for about four months after birth
* There is a very tight mother/calf relationship with narwhals
* There is not much information known about narwhal reproduction due to the fact that they are very difficult to study because they live in the arctic and they move around a lot
* Some scientists also believe that the males joust with their ivory tusks in order to court a fine female narwhal

Panthers are polygamous: they mate with more than one partner. Males will try to prevent other males from mating with females within their ranges but they are not always successful. Mating pairs may remain together for up to a week, sleeping and hunting together. Female panthers reach $exual maturity at about 1 1/2 to 2 1/2 years of age, and males at about 3 years of age.

Panthers, like all other cats with the possible exception of lions, are induced ovulators. This means that the stimulus of copulation triggers the release of the egg by the ovary. Induced ovulation is an adaptation for solitary cats to increase the probability that the egg will be fertilized (Mellen 1991). Humans and other more social species are spontaneous ovulators: they release eggs even in the absence of males.

A female will signify her $exual availability by the scent of her urine and by caterwauling, a yowl some people think sounds like the scream of a human female and which gave the panther the name screamer.